Seattle Times environment reporter Lynda Mapes and Times photographer Alan Berner are on the ground through the end of the week to report on protests of the Dakota Access Pipeline near Bismarck, N.D.

Hundreds of protesters have joined the Standing Rock Sioux tribe in their effort to block construction of the pipeline they say threatens water supplies and sacred sites.

American Indian tribes in Washington state on Tuesday called on President Obama to overhaul the way the federal government consults with tribes on fossil-fuel export and other projects. Also on Tuesday, the Obama administration asked for the second time that Energy Transfer Partners stand down on the Dakota Access Pipeline, to no avail.

Alfred Kills His Horse, 27, of the Lakota Nation, said he was standing on the front lines and was shot by a bean bag from a shotgun.

“The water is everything to us. I don’t understand why this chaos is coming to us. We all drink water,” he said. “I don’t want the violence. I don’t want to get shot. We don’t know any other way. We have been fighting the U.S. government for hundreds of years.”

Update, 2:09 p.m. (Pacific Time):

Protesters on horseback are galloping toward the front-line of the demonstration, wearing gas masks.

“They started advancing on our lines,” said Daniel Yellow Fat, Standing Rock Sioux tribal councilman. “They opened up a big gash on a man.”

Update, 1:58 p.m.:

Police are advancing with armored-personnel vehicle and ATVs. Campers are surrounded and outnumbered. Seven empty buses are en route while police move in.

Some protesters have locked themselves onto a pickup truck.

“You will be pepper sprayed if you do not get off of the pickup,” an officer said through a megaphone.

Update, 1:42 p.m.:

Police continue to work to clear the protesters’ camp on land owned by the Dakota Access Pipeline developer.

Update, 12:46 p.m.:

Police continue to push demonstrators south down the highway toward the protesters’ main camp about a half mile away. The front-line camp is owned by pipeline developers. Opponents began moving the camp there in the path of construction last weekend.

The first arrest on Thursday was made there as police encircle the camp, moving closer and closer, foot by foot.

“We need as much people as possible. They started spraying (pepper spray). They are pushing tents down,” said Devin Blackcloud, a Standing Rock tribal member. “No one is budging. There are 150, 200 people willing to be arrested.”

CANNON BALL, North Dakota (AP) – Armed soldiers and law enforcement officers dressed in riot gear on Thursday began arresting protesters who had set up a camp on private land to block construction of the Dakota Access oil pipeline.

Several protesters were led away and put in trucks, including at least one handcuffed, as authorities converged on the camp in North Dakota.

Law enforcement officers and soldiers driving trucks, military Humvees and buses began to advance at midday and formed a horseshoe-like loop once they reached the camp, where about 200 protesters were awaiting them — some defiant and other praying.

Officials used a loudspeaker to warn protesters to move out. Two helicopters and an airplane monitored the operation from the air.

The operation to push out the protesters began a day after they had refused to leave voluntarily.

UPDATE: Authorities trying to force Dakota Access protesters from a camp on private land in the path of pipeline construction are firing bean bags and pepper spray.

State Emergency Services spokeswoman Cecily Fong says officers are responding to "aggressive" tactics by protesters, including some throwing rocks at officers and threatening them.

Fong said she wasn't aware of any serious injuries to either officers or protesters.

A male protester was seen holding his leg after what an Associated Press reporter described as a loud boom. A protester with a medic bag tended to the man's leg, and he was up and walking a short time later.

Fong said she wasn't aware of any serious injuries to either officers or protesters.